Engine coolants utilized by the automotive industry for the cooling system of a vehicle usually contain ethylene glycol with a small percentage of diethylene glycol diluted with water to provide a 50% or lower concentration of glycol depending on the desired freezing point for the cooling system. Most companies that manufacture and/or distribute the engine coolants add corrosion inhibitors to the solution to prevent corrosion of the copper-brass materials traditionally used in the manufacture of vehicle radiators. These inhibitors usually are a mixture of one or more inorganic salts, such as phosphates, borates, nitrates, nitrites, silicates or arsenates, and an organic compound, such as benzotriazole, tolyltriazole or mercaptobenzothiazole, to prevent copper corrosion. The solution is generally buffered to a pH of 8-10 to reduce iron corrosion and to neutralize any glycolic acid formed in the oxidation of ethylene glycol.
Most manufacturers recommend a maximum of one or two years' service for their antifreeze coolant, however, the average car owner does not make an effort to follow the owner's instruction manual to maintain protection to -20.degree. F. for the coolant system, nor does the owner periodically check the coolant to determine if it is rusty or dirty. Many owners only add water to the coolant system when the antifreeze is lost through leakage or hose breakage.
In normal passenger car service, 25% of the new cars require coolant system servicing after only one year and, after two years, this percentage rises to 50%. In a conventional cooper-brass radiator, it is extremely important that the antifreeze or coolant mixture contain 50 to 55% of correctly inhibited ethylene glycol. A reduction in glycol concentration to a mixture of 33% ethylene glycol--67% water with a corresponding reduction in the inhibitor level will increase metal corrosion significantly. This is of special importance with higher temperature coolant systems which are becoming more common due to the increased use of emission controls.
Also, the increased emphasis on gas mileage for new automobiles has resulted in downsizing and weight reduction of the new cars. Weight reduction is accomplished through the substitution of lightweight metals or plastics for iron and steel in the body and other components of the car. For example, aluminum radiators may be utilized in automobile coolant systems in place of the copper-brass radiators previously used. An aluminum radiator appears to be more susceptible than copper-brass radiators to the corrosive action of a coolant or antifreeze that is low in the percentage of ethylene glycol and/or corrosion inhibitor present in the coolant. In such a system, additional corrosion inhibitor must be added or the aluminum will begin to pit at a rapid rate. The present invention ameliorates the corrosion problem by providing for the systematic addition of a corrosion inhibitor under corrosive conditions for the coolant.